Slip ring and brush assembly



' y 1958 L. c. BQLAND'ING 2,843,830

' SLIP RING AND BRUSH ASSEMBLY Filed Nov. 2, 1953 2 Sheets-Sheetl 5 Laxi INSULH T/OA/ l IN V EN TOR.

Zea/20rd GB/mzdi/z July 15, 1958 L. c. BLANDING SLIP RING AND BRUSHASSEMBLY 2 Sheets-Sheet 2 Filed Nov. 2, 1953 Ill d IlltlllII-lllllllll... llllllllll A I M INVENTOR. Leonard C. BlendingUnited States SLIP RING AND BRUSH ASSEMBLY Leonard C. Blanding, GrandRapids, Mich, assignor to Lear, Incorporated, Grand Rapids, Mich.

This invention relates to a slip ring and brush assembly of thesubminiature type wherein absolutely minimum friction and mass areimportant desiderata.

Many present day gyroscopic instruments, e. g. as used aboard aircraftin connection with horizon indicators and automatic pilots, involve theconduction of current between two or more relatively rotatable parts,and under circumstances where the use of flexible conductors iscontra-indicated. To provide the electrical connection various forms ofminiature slip ring and brush assemblies have been devised, and innearly all of these conventional practice has been followed. However,the generally known assemblies do not lend themselves well tominiaturization and therefore by using such constructions a lowerdimensional limit is reached which is still far removed from the desiredsituation.

I have found that by using a novel form of slip ring and brush, formingthe substance of the present invention, it is possible to provide agroup of thirty-two independently connected slip rings having a diameterof 0.140 and a length of 0.960" or an average space occupancy per ringaxially of 0.030 or close to inch.

Accordingly, the principal object of the invention resides in providinga subminiature slip ring and brush assembly having dimensionssubstantially less than similar assemblies heretofore known, hence lessinertia and lower friction torque.

Another object lies in providing an assembly as aforesaid in which theslip ring portion may be assembled with the brush unit without thehazard of damaging any of the brushes.

A further object resides in providing means for positive alignment of abrush with the ring individual thereto.

Still another object is to provide a subminiature slip ring and brushassembly which, notwithstanding the congested arrangement of parts iseasily accessible for wiring up in accordance with ordinary practice,and readily mounted on its supports.

Other objects will become apparent from the accompanying description anddrawings in which latter:

Fig. 1 shows the assembly with the brush portion sectionedlongitudinally;

Fig. 2 shows an end elevation viewed from the left of Fig. 1;

Fig. 3 is a cross section taken on the line 3-3 of Fig. 1;

Fig. 4 is a partial cross section taken on the line 4-4 of Fig 3;

Fig. 5 is a detail of a portion of a brush and its connecting lead;

Pig. 6 shows an endelevation of one of the brush supports; and

Fig. 7 is a partial cross section taken on the line 7-7 of Fig. 6.

In considering the description and the drawings it is believed that afuller appreciation of the scope of the invention will be had if thethought prevails that the important features of the invention take ontheir form stem 0 f 2,843,83d Patented July 15, 1%58 because of theextremely small dimensions involved. Put another way, a typicalembodiment of the invention utilizes a slip ring assembly of 32 ringsapproximately /s diameter and 1 long, and an exterior diameter of thebrush assembly of approximately Either the brush assembly or the slipring assembly may constitute the single rotating part, or both parts mayrotate, depending upon the application. Preferably, the slip ringassembly is made the rotating part because of possible adverse effectsof centrifugal force or momen' turn, or, in the case of both partsrotating, the slip ring assembly is preferably the part having the lowervelocity. A typical instrument to which the improvement of the inventionmay be applicable is disclosed in U. S. Letters Patent No. 2,595,951.

The slip ring assembly may, in general, take any of several well knownforms which may lend themselves to sub-miniature organizations, andtherefore as such form no part of the invention. Accordingly, a suitableassembly is indicated somewhat schematically in the several views as 10comprising slip rings 7 and insulating material 3 therebetween, and iscarried on a flange or hub 11 secured in any convenient manner to theparent part 12. However, notwithstanding the broad disclosure of theassembly 10 the free end 14 thereof is: preferably cylindro-ogival for apurpose to be explained.

The brush assembly (Fig. 1) in the example shown, comprises acylindrical shell 21 of metal having an internal shoulder 22 at one endand another shoulder 23 at the other, and which latter is preferably theresult of swaging or spinning over a portion of the shell following theinsertion of the brush units 25 which will secure the same firmly withinthe shell.

Referring to Figs. 1 and 3 particularly, each brush unit 25 comprises anelectrically-insulating annular body 26 including the circular aperture27 and a cylindrical recess 28. The marginal portion of the body 26 isperforated by a plurality of equally spaced bores 29 equal in number tothe maximum number of brushes to which the invention lends itself, inthis instance 36 in number. As will appear, the diameter of each bore 29is related to the size of the conductor to be threaded therethrough andto the size of the base circle upon which the bores are located.Obviously a larger conductor, therefore, will yield less holes for thesame diameter of base circle. At least one aperture, here shown as 2911opens directly into the recess 28 by means of a V-shaped cutout 32 (Fig.6).

Each of the brushes 41 is arranged for wiping action on twodiametrically opposite points of a slip ring to provide balanced tensionbetween the two arms of the brush and, secondarily, to insure, in caseof damage or error in manufacture, that at least one arm will havecontact. Thus, a brush comprises resilient wire, e. g. Phosphor bronzeincluding two parts 42 and 43 (Figs. 4 and 5) soldered together, as at44. Preferably the adjoining elements of the parts 42 and 43 are leftunsoldered over a short distance, such as X, to afford freedom oftorsion about the axis of each wire as the brush arms are flexed inassembly and use. Each part 42 and 43 includes, in the confines of therecess 28, an arm or finger 46-46 so proportioned as to result in eachthereof being tangent to the associated slip ring at the ends of adiameter, although such precise considcration is not essential. It willbe observed that the portions of each part 42 and 43 joining the finger46 to the axially-extending portions cliverge slightly in the vicinityof the cut-out 32 in order to permit flexing movement thereof, and tolimit the minimum spaced position of the fingers 46. Stated otherwise,upon withdrawal of the slip ring assembly the tension of the brusheswill urge them to assume a position indicated by the outer set of dottedlines, and as limited by a pair of projections 5151 extending from thefloor of the recess 28. Obviously it is desirable to maintain thefingers 46-46 sufliciently far apart to permit the nose 14, uponre-assembly, to pass between the fingers 46 without risk of deformationthereof.

As will now be apparent each brush is provided with an individual one ofthe bores 29 for passage of its related parts 42 and 43 (Fig. 4).Clearance for the brush fingers is afforded within the recess 28.

One of the important advantages of the invention resides in theintegration of the brush and its conductor. Accordingly, parts 4344 arecarried around an electrically insulating layer 61, e. g. plasticcompositon, formed on a flange 62 extending from the cylinder 21.Supplemental anchorage of the layer 61 may be accomplished by providingapertures 64 in the flange 62 and molding the composition therewithin asshown. As part of the molding operation aforesaid a plurality ofterminal lugs 67 of U-form may be included and thereby rigidly carriedon the flange 62 and simultaneously electrically insulated. Followingpreparation of the brush support including the terminal lug 67 each partor conductor 43 may be wound around and soldered to one of the legs of alug, and the leg thereafter bent over as additional security. The leads,

such as 71, from the component to which a brush relates may be similarlysoldered and anchored to the other leg of the terminal lug.

Although the flange 62 is shown in the example as frusto-conical this isonly for considerations involved in a particular application. However,it is essential, in a subminiature assembly to fan the leads radially(Fig. 2) to provide working clearance at the lugs 67.

It will have become clear that the invention lends itself ideally tounits having one or a large number of brushes. Each brush and itsassociated holder 25 is an independent subassembly. For example, thecylinder or housing 21 may be simply decreased or increased in length inaccordance with the number of brush units or, if a standard length ofcylinder 21 appears to be desirable from a manufacturing or inventorystandpoint holders 25 may be utilized as dummies.

For clarity Figs. 1 and 2 show only a single conductor representing thepair of conductors 43 and 44.

By virtue of the minimal dimensions achieved in the instant constructionthe assembly may be readily fitted within the bearing of a gimbal joint,and space-consuming protrusion exteriorly of the joint thereby avoided.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made, and I therefore contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

I claim: p

1. A slip ring and brush assembly comprising a slip rlng arbor, aplurality of slip rings carried on said arbor and having active facesflush therewith, means at one end of said arbor for rotatably supportingthe same, the opposite end of said arbor having a tapered nose, an equalplurality of electrically-insulating brush housings of hollow,cylindrical form and a casing for supporting said housings inface-to-face relation, each housing having an annular recess in oneradially-disposed, flat face thereof and the central opening of eachholder being of greater diameter than the rings, a brush individual toeach housing located in said recess for wiping on an associated slipring, each brush including a pair of fingers for tangential contact withthe ring substantially at the opposite ends of a diameter thereof, anaxially-extending conductor for each brush, and said holders as a grouphaving aperture means for passage of said conductors, said brush beingradially resilient and having, in the absence of the slip ring, arelaxed position within the area of said central opening and, in thepresence of the slip ring, an operative position substantially outsidethe area of said opening, said recess providing a guide for radialmovement of the brush but restraining the brush against appreciablemovement axially whereby the slip ring arbor may be moved axially intoand out of operative relation with the brushes without damage thereto.

2. A brush assembly in accordance with claim 1 wherein said aperturemeans comprises a plurality of bores distributed around the end faceportion of a holder surrounding the recess therein, the bores of allholders being in alignment and each aligned plurality receiving theconductor of a single brush.

3. A brush assembly in accordance with claim 1 wherein each said brushcomprises two resilient wire members each formed to provide a saidfinger and cojoined over a common portion of each to provide a unitarybrush, one of said portions being extended to provide a conductor forconnecting said brush to the electrical component with which the brushis associated.

4. A slip ring and brush assembly comprising an arbor having a pluralityof axially spaced-apart slip rings, a cylindrical sleeve having aradially-extending flange at one end thereof, a like plurality ofhollow, cylindrical brush holders retained in said sleeve inface-to-face relation, each said holder having an annular recess in oneradially disposed face thereof providing an annular space with theabutting holder, a bifurcated resilient wire member positioned in eachsaid space, the furcations whereof are so formed and tensioned as tobear on opposite sides of the slip ring associated with the brush, saidarbor having a tapered end for facilitating assembly of the arbor withinthe group of brushes, said end being constructed and arranged to passbetween said furcations and to separate them without injury, each brushbeing provided with a projection at the junction of the furcations,extending perpendicularly to the plane of the brush, each said holderhaving an aperture for receiving said projection to prevent rotation ofa brush on the axis of the holder, a conductor joined to saidprojection, each said holder having a plurality of axially extendingaligned bores for passage of said conductors, said conductorsterminating at a common end of said sleeve and said sleeve beingprovided with a radially extending flange at one end thereof, a layer ofelectrically insulating material on the outer face of said flange, aplurality of U-shaped terminal lugs secured in said layer by imbedmentof the bight of the U and the legs thereof protruding outwardly of saidlayer, the terminus of each conductor being connected to one leg and theseveral other legs serving for connection of the external, incomingconductors.

References Cited in the file of this patent UNITED STATES PATENTS SwedenJune 20, 1944

